The present invention relates to processes and apparatus for the continuous preparation of preshaped single crystals, and more particularly, this invention relates to methods for the preparation of preshaped single crystals through the use of a crucible provided with a pendant drop capillary, so that little or no machining of the single crystals produced is required.
There are a number of methods for preparing single crystals, notably the Verneuil process and its modifications, which are described for example in the article by F. A. Halden and R. Sedlacek entitled "Verneuil Crystal Growth in the Arc-Image Furnace" published in Review of Scientific Instruments 34(6) (June 1963); the Czochralski method described in the R. A. Laudise contribution The Growth of Single Crystals, published in the Solid State Physical Electronic Series, Prentice Hall, New York, 1970, edited by Nick Holonyack, Jr. The Czochralski-type processes involve vertically pulling a crystal starting from a molten bath by means of a single seed crystal turning around itself.
These processes lead to single crystals having bulky geometric shapes such as cylinders or cones, requiring considerable and delicate machine-finishing to obtain single crystals in a useful form, usually a thin slice. Moreover, these processes require a hiatus in the procedure every time the available liquid in the crucible is exhausted.
What is more, these prior art processes require crystallization vessels of very considerable size, on the order of several liters, and this constitutes a major drawback because the vessels are fabricated from rare metals, such as iridium, and are expensive. In use, these containers have a limited life of only a few crystallizations because of the chemical and thermal corrosion to which they are subjected, and this considerably increases the cost of producing such single crystals.